diff --git a/Readme.md b/Readme.md
index b854f24..31a3d14 100644
--- a/Readme.md
+++ b/Readme.md
@@ -11,3 +11,24 @@ Webserver with CGI enabled
 + run the modelbahn-server application.
 
 ![Screenshot](https://steffen.gulpe.de/progs/modelbahn.png)
+
+
+## Z21EMU and ATmega Sensors
+
+Per default all devices get the same I2C defive address. As soon as the device is connected you should set up a new address for them. The following commands will set the device [0x2f] to address 0x31 and save this setting in the EPROM.
+
+	i2cset -y 1 0x2f 0x22 0x31
+	i2cset -y 1 0x2f 0x21 0x02
+
+The following registers are used:
+
+	0x00 .. 0x08 INPUT and OUTPUT registers dependung on device
+	0x20         VERSION of the device
+	0x21         Command Register
+					0   no command
+					1   EEPROM read
+					2   EEPORM write
+	0x22         I2C Address
+	0x23         Input Off Delay
+
+